Synthesis and X-ray and Spectral Study of the Compounds [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me, Et, n-Pr, n-Bu)

Iron nitrosyl complexes with general formula [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me, Et, n-Pr, n-Bu) were synthesized by the exchange reaction of K2[Fe2(S2O3)2(NO)4] with tetraalkylammonium bromides. The molecular and crystal structure of [(CH3)4N]2[Fe2(S2O3)2(NO)4] were studied by X-ray diffraction analysis. The iron atom in the four-membered cycle of the [2Fe–2S] anion is bound to another Fe atom and to two sulfur atoms and is coordinated by two nonequivalent NO groups, each bridging sulfur atom being bound to the SO3group. The structurally equivalent iron atoms are in the state Fe1–(S= 1/2). The Mössbauer spectroscopy method shows that the complexes are diamagnetic due to the strong Fe–Fe bond. It is found that the SO3group provides higher stability of the thiosulfate anion than the anion in Roussin's red salt [Fe2S2(NO)4]2–.